1. Field of the Invention
The present invention relates to an injection molding method and an injection molding device that inject a molding material such as resin, glass, and metal into a mold and also perform an operation to open the mold before or after the injection by a predetermined amount. More specifically, the present invention applies to an injection molding method that injects a molding material such as resin, glass, and metal while a mold is open by a predetermined amount and then provides a compressive force to the molding material by closing the mold or an injection molding method for foam molding by injecting a molding material into a mold and then opening the mold by a predetermined amount. In particular, the present invention relates to control to mold a molded product with low distortion or without welding and a technology capable of stabilizing the molded product at an early stage and continuing to mold with stability for a long period of time.
2. Description of the Related Art
An injection molding method is generally known as a method for molding by injecting a molding material such as resin, glass, and metal into a mold (see Jpn. Pat. Appln. KOKAI Publication No. 2003-136569, for example).
An injection compression molding method, which is a kind of the injection molding method, is widely used when optical products such as lenses requiring a precise form transfer or molded products in a large flat-plate shape are molded with low distortion. The injection compression molding method is a molding method for molding a product by filling a mold immediately before mold closing with a molding material and then closing the mold completely.
According to such a molding method, a mold is open by a predetermined amount in advance before injection so that fluidity of a molding material is improved, enabling efficient filling. After that, molded products in which molecular arrangement of the molding material is improved and having less pressure gradient and less distortion therein can be obtained by applying pressure to the molding material through compression.
In the injection compression molding, the position in which a mold is stopped immediately before mold closing (hereinafter, referred to as a “micro mold-open position”) affects the pressure and the like during mold closing and so is precisely determined in advance based on the shape of a molded product, the molding material to be used, injection pressure and the like.
On the other hand, if pressure during mold closing is too high, the mold could be damaged. Thus, if, for example, the temperature of the mold rises and the mold-closing position of the mold fluctuates, the mold-closing position is changed in such a way that a mold-closing force becomes a desired value. If, in a mold-clamping device using, for example, a toggle mechanism, the mold-closing position fluctuates due to a temperature rise, adjustments are made in such a way that the mold-closing force during mold closing becomes a predetermined value by changing the stop position of a crosshead of the toggle mechanism.
However, even if the mold-closing position is changed in response to changes in temperature or the like, the micro mold-open position to keep the mold slightly open immediately before mold closing is not changed. Thus, a changed mold-closing position results in a shift of a micro mold-open amount (hereinafter, referred to as a “position shift”) with regard to the mold-closing position. Accordingly, the filling amount fluctuates due to a change in filling resistance of the molding material and so the weight of molded products fluctuates, which makes it impossible to obtain molded products with stable quality.
To resolve the position shift, a control mechanism is separately needed to exercise feedback control using a position sensor provided in the mold and so on. However, if the position sensor is provided in the mold, there is a problem of increased costs and also a problem of a longer setup time before starting molding such as needed work to connect the sensor. Further, it is necessary to mount the position sensor on the mold and if the mold operates at high temperature, the position sensor is affected by the temperature, leading to decreased reliability.